Magnetic core for electrical apparatus



May 19, 1931. M. o. TROY 1,805,534

MAGNETIC CORE FOR ELECTRICAL APPARATUS Filed Dec. 18, 1929 Fi I. /7 gFig.5.

Inventor: Matthew OTroy, by Hi S Attorney Patented May 19, 1931 UNITEDSTATES PATENT OFFICE MATTHEW O. TROY, OF SCHENECTADY, NEW YORK, ASSTGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK MAGNETICCORE FOR ELECTRICAL APPARATUS Application-filed December 18, 1929.Serial No. 415,003.

My invention relates to magnetic cores for electrical a paratus such astransformers and reactors. uch cores are generally formed of superposedsheets or laminations of magnetic materlal, the laminations beingannealed to 'improve their magnetic characteristics and being insulatedfrom each other to reduce eddy current losses. The magnetic materialmost commonl used is a high grade of silicon 19 steel. There iiave beendeveloped however certain other materials, such as nickel iron alloys,which have better magnetic characteristics butaresomuch more expensiveas to prohibit their general use. It has been proposed therefore to usethe better but more expensive material in the part of a magneticcoreiwhere it will do the most good, the remainderof the core beingformed of less expensive material to keep down the final cost of theentire core.

:0 The .greatest advantage is obtained by using the better magneticmaterial in that part of the core which is surrounded by a winding orwindings because the space for the material is limited. 'In those partsof the core which are outside the winding or windings, the space is notlimited and magnetic losses may be kept down by using an ample amount ofthe less expensive material. "This is explained in United States PatentNo. 1,698,634

to S. E. J ohannesen, issued January 8, 1929. The general object of thepresent invention 9 is to provide an improved magnetic core constructionincluding two grades of magnetic material, the material having thebetter magof the core which is surrounded by a winding or windings. I

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawings in which Fig. 1 showsa transformer having a magnetic core constructed in accordance with theinvention, and Figs. 2, 3, 4 and 5 show various forms of laminationsections which may be used in the core shown in Fig. 1.

Like reference characters indicate similar parts in the diflerentfigures of the drawings.

The invention will be explained in connection with the transformer shownin Fig. 1. 60 This transformer has a magnetic core formed neticcharacteristics being used in that part I in two parts 10 and 11, bothparts being of hollow rectangular shape placed edge to edge and withtheir adjacent sides surrounded by a low voltage winding 12 and a highvoltage winding 13. Each of the parts 10 and 11 of the core is built upas usual of a plurality of superposed layers or laminations of magneticmaterial. Adjacent layers should of course be insulated from each otherto prevent excessive eddy currents.

Each of the layers or laminations of each part of the core includes twoL-shaped sections 14 and 15. Each section 15 has a long outer legportion 16 and a shorter yoke portion 17. Both of these portions 16 and17 may be as wide as desired so that there will be ample material inthese parts of the core to keep down the magnetic losses. Verysatisfactory and economical methods, such as is disclosed in UnitedStates Patent No. 1,334,149 to J. J. Frank, issued March 16, 1920, havebeen proposed for producing L- shaped magnetic sheet punchings and thesections 15 may be produced by any method desired.

Each of the lamination sections 14 includes a winding leg portion 18 anda yoke portion 19. Each of these portions 18 and 19 is a straight pieceof material with parallel side edges and may obviously be cut or punchedfrom large stock sheets with very little waste. The stock sheets areproduced by a rolling process while heated and this results in a grainin the direction in which the sheets are rolled. It is well known thatthe best results are obtained if the path of the magnetic flux in thefinished core is in the directien of this grain so the edges of theportions 18 and 19 are preferably parallel to the grain formed in theseportions by the rolling process used in forming the stock sheets fromwhich they were cut or punched. The grain will therefore extendlongitudinally of each of the portions 18 and 19.

The portion 18 of each lamination section 14 is surrounded by thewindings 12 and 13 and is formed of a. high grade of magnetic materialsuch as a nickel iron alloy. The magnetic losses in this winding legpart of the core are therefore kept to a low value by the use of a highgrade expensive material in the limited space available for it. Theportion 19 of each lamination section 14 is formed of a cheaper magneticmaterial such as silicon steel the losses being kept down in this yokepart of the core by making these portions 19 of ample Width to providean ample amount of material.

The portions 18 and 19 of each lamination section 14 are fitted togetherand united into an integral unit by a weld 20. The welds may be of anydesired form, several varia tions being shown in the different figuresof the drawing. The portions 18 and 19 may have straight meeting edgeswhich are welded together-as indicated in Figs. 1, 2 and 3 or they mayhave toothed edges welded together as indicated in Figs. 4 and 5. It hasbeen found that the toothed edges permit the strongest Weld to be made.Alternate laminations or alternate small groups of them are preferablyreversed endwise as usual so that the joints between the sections 14 and15 will be at different places in the core.

A core such as has been described consists entirely of simple L-shapedlamination sections formed of two grades of magnetic material, thebetter and more expensive material being restricted to the winding legof the core where it is of greatest advantage.

The invention has been explained by describing and illustrating aparticular form thereof but it will be apparent that changes may be madewithout departing from the spirit of the invention and the scope of theappended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. A transformer core including magnetic laminations formed of a highgrade expensive material and a lower grade less expensive material, thewinding leg portion of each of said laminations being formed of the highgrade material and being welded to a yoke portion formed of the lowergrade material to form a unitary lamination section, the ends of each ofsaid lamination sections being connected by an L-shaped laminationsection of the lower grade material.

2. A transformer core lamination in the form of a hollow rectangle, oneside of said rectangle being formed of a high grade ex pensive magneticmaterial welded to an adiacent side of the rectangle to form a unitaryL-shaped lamination section, said adjacent side being formed of a lowergrade less expensive magnetic material, and the ends of said laminationsection being connected by an L shaped lamination section of the lowergrade magnetic material forming the other two sides of said rectangle.

3. A core lamination section including a straight winding leg portion ofhigh grade expensive magnetic material, and a straight yoke portion oflower grade less expensive magnetic material, said two portions beingwelded together to form a unitary L-shape nected together by a weldedjoint, one of said I portions being of high grade expensive rolledmagnetic material and the other portion being of lower grade lessexpensive rolled magnetic material, and each of said portions hav ing agrain produced by the rolling process ezfitending substantiallylongitudinally there 0 In Witness whereof I have hereunto set my handthis 17th day of December, 1929. MATTHEW O. TROY.

